The Theatre of the Face: Portrait Photography Since 1900 by Max Kozloff 416pp, Phaidon, £39.95

In the winter of 1938, Walker Evans began a series of candid portraits of passengers on the New York subway. His overcoat protected him against the cold and, more importantly, concealed the 35mm Contax strapped to his chest. The camera had been painted matt black and was operated by a shutter release cable that ran down his right sleeve. Evans was not averse to tricks and decoys to get a picture; even so, the level of subterfuge was unusual. But perhaps it was the only way to capture the slack-jawed and vacant moments when his fellow commuters' faces were in what he described as "naked repose" when "the guard is down and the mask is off".

The conventions of early studio photography had long been redundant, and portraiture had been invigorated by its contact with the more spontaneous modes of documentary and news photography, yet still the face remained a site of drama, display and artifice. Evans, America's foremost documentary photographer, wanted to capture the intermission not the performance.

His work is among that chronicled in Max Kozloff's The Theatre of the Face, a study of the development of portrait photography through the 20th century to the present day. It is significant that the photographers Kozloff includes are often a good deal more famous than their sitters. There are taxi drivers and barmaids here, sailors and majorettes, hustlers, sharecroppers and vagrants. Teenagers and prostitutes outnumber statesmen. Kozloff favours anonymous faces and everyday locations: he makes room for discarded strips of photo booth portraits, but not for the celebrated sitters of Karsh, Bailey, Leibovitz or Testino.

Of course the subject's performance has always had to contend with that of the photographer, also engaged in mounting a production of sorts. Edward Curtis, for example, would use props, wigs and costumes to ensure that the indigenous tribes he recorded conformed to his own expectations of their attire. Brassaï's apparently spontaneous shots of "secret Paris" required an assistant, magnesium flares and a tripod-mounted camera. And Robert Coburn's mask-like portrait of Merle Oberon was deliberately lit to conceal the scars left by make-up poisoning.

Kozloff's account of the shifting and diverse terms of engagement between photographer and sitter is informed by an awareness of the moral implications of the relationship. Lewis Hine's reformist photographs of child labourers in appalling workplace conditions at the turn of the century, for example, manifest a concern and a respect that is congruent with Hine's social activism. The simplified compositions and frontal poses - arrangements popularised by news photography - constituted a pictorial appeal that was understood to be both direct and honest.

Given the preponderance of American photographers included here, it is perhaps surprising to note that the longest shadow cast is that of August Sander and his monumental, unfinished project of the Weimar era, "People of the 20th Century". Unlike Hine, Sander's avowed goal was to see "things as they are, and not as they should be". "People" comprised a series of portraits that Sander believed represented different social types defined by class position or function. Colonels, farmers, Nazis and circus performers were all photographed with a studied and uniform neutrality. This elimination of any trace of condescension or valorisation - and, to an extent, any trace of his own authorship - was not lost on his contemporaries. Responding to the scientific and objective aspects of the project, Walter Benjamin likened it to an atlas or training manual. Evans hailed it as a "photographic editing of society - a clinical process".

Though Kozloff expresses unease at the estranged and ambivalent tone of Sander's work (on the grounds that it could amount to quietism), he concedes the enormous impact an aesthetic of objectivity has had on subsequent photographers, among the most illustrious of whom, in this account, is Richard Avedon.

But in Avedon's work Kozloff detects what he terms a "creative misreading" of Sander's detachment, which now takes the form of an overdramatised and callous disengagement that - far from allowing the subjects to unambiguously present themselves to the camera - overwhelms those it surveys. The high contrast lighting and printing of Avedon's pictures serve to expose every blemish, so that even the face of his dying father is rendered "like spoiling fruit". Though he concedes Avedon is among the most gifted of his generation, and his images among the most forceful, his photography is, says Kozloff, the expression of an invasive opportunism. When photographing the dog-loving Duchess of Windsor in 1957, Avedon mentioned that his own pet had just been run over - as her face registered the news, the shutter opened.

Much of the most innovative (and narcissistic) portraiture in recent decades has been made by artists using photography to explore questions of representation, gender and identity. Cindy Sherman's "Untitled Film Stills" - a series of self-portraits in guises and scenarios parodying popular culture - is the most celebrated example. In many respects her work represents a radical engagement with Kozloff's main themes. Not only do her pictures thoroughly enmesh the regard of the photographer and the attitude of the subject, but her extravagant use of disguise and charade effectively negates any readable autobiographical content.

Early photography required sitters to pose motionless for long periods under the glass roofs of brightly-lit studios; Roland Barthes likened the process to incarceration in a museum. The Theatre of the Face charts portraiture's emergence and development as a dynamic, vivid and unpredictable exchange between photographer and subject. Of course the field is vast, and any selection will be partial. Kozloff's history is humanistic, not sociological. It is also astute, nuanced, accessible and, not least, intelligently designed. Ultimately, though, its most persuasive recommendation is the sheer quality, originality and diversity of the portraits themselves.